The invention relates to the art of rotary engines and more particularly to a rotary engine having an exterior rotary output member driven by opposed pistons housed within a stationary cylinder or stationary in-line cylinders.
The reciprocal internal combustion engine, as those skilled in the art are well aware, is the result of at least 75 years of technological progress. The method of converting heat energy input to mechanical energy output, while regarded today as highly developed, is less efficient than is possible since conversion of the heat energy to mechanical energy is done through the piston, connecting rod and the crankshaft to the rotating output member. This is true whether the internal combustion be by spark ignition or by compression ignition. The losses in the system are well recognized and have been extensively examined over the years. The inefficiency of the connecting rod-crankshaft piston engine is one of the reasons why a good deal of effort has been turned since World War II to the development of the rotary, turbine and other types of compact power units.
The constraints imposed by connecting rod, crankshaft type engines are numerous. Connecting rod length and crank radius with their fixed interrelationship to the piston are the primary contraint factors and exert a profound influence on the piston travel function and ultimately on the engine performance. The rapid piston motion, rise to and fall from top dead center, at speed, present the greatest problem to the engine designer since ignition must occur prior to the engine's achieving full compression so as to provide time to reasonably complete burning which continues while the piston moves away from top dead center. Thus, the connecting rod and crankshaft constraint effectively prevents achievement of constant volume combustion of the ideal cycle. A substantial amount of heat is lost from the combusting fuel or working fluid because of the relatively slow expansion process which is determined by the interrelationship of the connecting rod, piston and crankshaft. Additionally, in conventional reciprocating piston engines the exhaust valve will be opened before the piston has reached bottom dead center thereby causing additional loss of energy.
In combusting the compressed fuel and thus providing energy to do work on the piston much energy is lost through the cylinder head as waste heat. Energy is lost because of the amount of surface area exposed to direct flame during combustion process and combustion must be started before the piston reaches top dead center, causing the piston to compress an already expanding gas. Energy dumped into the coolant of a conventional engine, as waste heat, may be up to as much as 60% of the total energy available from the burning fuel.
The linear piston movement in the power stroke is the initial conversion step from heat energy to mechanical energy. The linear motion is in turn converted to the angular motion of the connecting rod which in turn develops the circular motion of the crankshaft. Each of these components subtracts from the final energy output and is a design which is completely unbalanced. Balance is achieved with the addition of compensating weights. Any excess weight which must be designed into the engine in the form of counterweights, flywheels and other compensation features and frictional losses associated with the motion of such parts uses up energy to lessen engine efficiency.
As is well known, a four stroke cycle engine turns its crankshaft 720.degree. from combustion stroke to combustion stroke on a given cylinder. A two stroke cycle engine turns its output shaft 360.degree. from combustion stroke to combustion stroke. In either the four stroke cycle or the two stroke cycle engine the distance in degrees rotation, from the point of applied energy to the output, is large since the design of the mechanical system, in the case of the four stroke cycle, is such that for each positive power stroke of the piston there are three (3) negative strokes the piston must go through. Further the length of the connecting rod and the diameter of the crankshaft are directly related to the stroke of the piston. In net effect, there has been a great need in the automotive industry to develop a different engine, initially for higher specific power output per pound of weight and more recently to improve mileage and reduce pollution.
There are fundamental reasons why the industry has not leaped into new engine production. Among those are the fact that most engine cycles lead to larger and more expensive units than conventional power plants and are of such design that they radically depart from known technology. This is particularly true of external combustion engines. Further, of the immediate reasonable alternatives, such as for example, the Wankle rotary or the gas turbine, each has difficulties. The Wankel which is a compative engine for small vehicles does not economically scale upwardly in power, and it is an example of radical departure from known technology. The turbine which is competitive for large vehicles does not scale down in power or size economically. However, the internal combustion engine does not burn fuel completely, is very complex and its mechanical and thermal efficiency leaves much to be desired to say nothing of its fuel consumption and horsepower loss.
Among the prior art references considered to be of interest are U.S. Pat. Nos. 1,252,757; 1,485,988; 1,533,514; 2,149;591; 3,688,751; and 3,874,348.